Combustion turbines generally comprise a casing for housing a compressor section, a combustor section and a turbine section. Each one of these sections comprise an inlet end and an outlet end. A combustor transition duct is mechanically coupled between the combustor section outlet end and the turbine section inlet end to direct a working gas from the combustor section into the turbine section.
The working gas is produced by combusting an air/fuel mixture in one or more combustors located in the combustor section. A supply of compressed air, originating from the compressor section, is mixed with a fuel supply to create a combustible fuel/air mixture. The fuel/air mixture is combusted in the combustor to produce a high temperature and high pressure working gas. The working gas flows from the combustor through the combustor transition duct into a first stage of the turbine section.
Destructive acoustic pressure oscillations or pressure pulses may be generated in the combustor as a consequence of normal operating conditions depending on fuel/air stoichiometry, total mass flow, and other operating conditions. In accordance with current design practices to lower NOx emissions required to meet federal and local air pollution standards, leaner premixed combustion systems are typically used in which fuel and air are mixed homogeneously upstream of the flame reaction region, and in which the fuel/air ratio or the equivalence ratio at which these combustion systems are operated is much leaner compared to more conventional combustors in order to maintain low flame temperatures which in turn limits production of unwanted gaseous NOx emissions to acceptable levels.
Although this method of achieving low emissions is widely used, there is a combustion instability which may occur during operation at low equivalence ratio, tending to create unacceptably high dynamic pressure oscillations in the combustor. Dynamic pressure oscillations or pressure pulses can result in mechanical and thermal fatigue to combustor hardware.
The present invention addresses the problem associated with dynamic pressure oscillations in a gas turbine engine combustor by providing an acoustic filter for attenuating the energy associated with the pressure oscillations.